This invention relates generally to a system for imaging objects to be scanned, and in particular, it relates to a high-speed, document-imaging system which utilizes an apparatus for evenly illuminating the documents being scanned.
Today, there is an increasing trend to automate the processing of documents, as for example, the processing of checks and related documents in a financial environment. Part of this processing relates to "imaging" documents as they are moved along a document track. The images of the documents are then viewed, sequentially, on a video terminal where an operator performs data completion, such as "keying in" the monetary amounts for individual checks, for example.
The imaging of the documents is generally performed by scanning a portion of a document along a scanning line as the document is moved in a document track. The scanning line is illuminated, and an optical system is used to direct the light reflected from the document at the scanning line to a light-sensitive detector. The detector is generally a light-sensitive, solid-state array which may include for example, 1024 pixels (picture elements or individual detectors) which are aligned in a vertical column. The length of the column or array is generally slightly longer than one inch while the length of the scanning line is slightly longer than four inches to accommodate the variety of checks to be processed as received at a bank. The individual detectors in the array produce a gray scale value which corresponds to the associated portion of the document at the scanning line. The gray scale values may be one of 64 values ranging from pure white to solid black, for example. These gray scale values are "thresholded" by additional processing circuitry by converting the gray scale value of an individual pixel into either a binary zero (white) or a binary one (black), for example. The binary values for the pixels in a scanning line are stored in a memory along with the data for other scans which comprise the image data for the entire document. The image data for a document is then withdrawn from memory and "reconstituted" to present an image of the document on a video terminal for use as earlier described herein.
In order to have accurate thresholding of data from the system described, it is very important to have the scanning line illuminated by an even intensity of light over the entire length of the scanning line. Uneven lighting at the scanning line complicates the thresholding circuitry and produces inaccurate or incomplete images of the documents when displayed on a video terminal.